1. Field of the Invention
The present invention relates generally to a method and an apparatus for digital up-down conversion using an Infinite Impulse Response (IIR) filter, and more particularly, to a method for digital up-down conversion for reducing a delay time greater than a delay time in a structure using a conventional Finite Impulse Response (FIR) filter by applying a decimation filter and an interpolation filter used in up-conversion and down-conversion procedures in a relay system as an IIR filter structure, and an apparatus thereof.
2. Description of the Related Art
A conventional service enterpriser establishes infrastructure, through extension of a base station, in order to provide various high-quality wireless communication services to a user. However, as the number of service subscribers has increased, in order to maintain service quality, most communication service enterprisers have installed and managed a relay capable of increasing communication network coverage for a shade zone, which has relatively lower installation and maintenance costs than installation and maintenance costs of a conventional base station, which typically has a high cost as a main communication infra construction method. Such a relay system functions as a relay between a base station and a user. The relay system amplifies a received signal that has a weak power due to various reasons such as a distance from a base station and a channel environment, eliminates interference from the amplified signal, and transmits the amplified signal back to a user.
Meanwhile, in recent years, mobile communication systems have been using Orthogonal Frequency Division Multiplexing (OFDM) to increase a transmission rate of signals. A system using OFDM as a modulation technology requires a guard interval between symbols in order to prevent deterioration of performance caused by intersymbol interference. The guard interval is determined considering a delay spread. Accordingly, as a transmission delay occurs between a transmitting end and a receiving end, when the delay spread becomes larger than the guard interval of the OFDM, intersymbol interference occurs in demodulation of a receiving procedure.
Accordingly, a delay time occurring between a transmitting end and a receiving end, in particular during a relay procedure causes intersymbol interference, thereby degrading system performance. Therefore, there is a need for a scheme for reducing a delay time of the relay so as to prevent degradation of the system performance.
In particular, an element having a most significant influence on a time delay in a conventional relay system is processing delay times of a decimation filter and an interpolation filter used during up-down conversion procedures. A general FIR filter has a disadvantage, in that the general FIR filter cannot reduce a delay time below a given limit while maintaining a magnitude response characteristic of a filter during a processing procedure of a relay system due to an original delay and a processing delay time.
Consequently, there is a demand for a method of reducing processing delay times of a decimation filter and an interpolation filter with an FIR filter.